1. Field of the Invention
This disclosure relates to polymeric interlayers and, in particular, to polymeric interlayers suitable for use in, for example, in multiple layer panels.
2. Description of Related Art
Poly(vinyl butyral) (PVB) is often used in the manufacture of polymer sheets that can be used as interlayers in multiple layer panels, including, for example, light-transmitting laminates such as safety glass. Safety glass generally refers to a transparent laminate that includes at least one polymer sheet, or interlayer, disposed between two sheets of glass. Safety glass is often used as a transparent barrier in architectural and automotive applications, and one of its primary functions is to absorb energy resulting from impact or a blow without allowing penetration of the object through the glass. In cases when the applied force is sufficient to break the glass, the polymeric interlayer disposed between the panels retains the sharp glass shards, which minimizes injury and damage to people or objects within the area enclosed by the glass. Safety glass may also provide other benefits, such as a reduction in ultraviolet (UV) and/or infrared (IR) radiation, and it may also enhance the aesthetic appearance of window openings through addition of color, texture, and the like. Additionally, safety glass with desirable acoustic properties has also been produced, which results in quieter internal spaces.
Interlayers used to form acoustic glass panels may include a single “core” layer sandwiched between two outer “skin” layers. Typically, the core layer is a softer layer having a lower glass transition temperature than the outer skin layers. Use of a softer layer enhances the ability of the interlayer to dissipate acoustic energy of the vibrating structure, thereby minimizing the transmission of sound through the panel. In order to sufficiently minimize sound transfer, the core layer of an acoustic interlayer must be thick enough to allow transverse shearing to take place within the laminated structure. Tri-layer acoustic interlayers with an insufficient core layer can fail to provide adequate sound dampening performance.
Multiple layer panels, including those formed with glass substrates, that utilize conventional acoustic interlayers may, under extreme processing and/or environmental conditions, develop visual defects called “iceflowers” or “snowflakes.” These types of defects form in the presence of elevated temperatures and when excess air is trapped within the laminate and, more particularly, within the softer core layer. When a laminated panel is subjected to elevated temperatures and/or glass stress, any pockets of air remaining in the interlayer may form bubbles, which nucleate in the softer core layer and then spread throughout the polymer layers when the panel is exposed to extreme conditions. These types of defects are particularly problematic when the substrates used to form the multiple layer panel include mismatched glass, such as, tempered glass, heat strengthened glass, annealed glass panels, as well as glass panels having significant curvature, like windshields, that form so-called “bending gaps” where air pockets can accumulate.
Thus, a need exists for a multiple layer interlayer that resists defect formation, including iceflowers, while still exhibiting good optical properties and suitable acoustic performance. Such interlayers should be usable in a wide variety of applications, including automotive and aeronautical safety glass, as well as architectural panels and other polymeric laminates.